Identification of Cracks

What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

1a)

In the above image it is observed that the concrete is crushed and the reinforcement is also exposed at the bottom portion of the beam. The cracks were initiated from bottom of the beam and propagated upward. Concrete spalled beyond the reinforcement which may be a sign of rupture. The beam top portion looks safe because of the flange advantage from slab. Flexural damage is mostly associated with cracking and spalling of concrete and yielding of the reinforcement. The crack develops from bottom to top means rebar yielding occurs in support bottom only. This is a Flexural failure of beam due to reversal of stress during earthquake. During stress reversal, beam top experiences compression and bottom experiences tension. Top compression is managed by slab advantage. But bottom tension was not satisfied by the provided reinforcement. Since the reinforcement got yielded, it cannot be repaired.

1b)

In the above image it can be seen that the cracks were along Beam-Column edge. Cracks seem to have developed through the structure as it looks much wider. It can be observed that the beam looks separated from the column at joints. The concrete is not severely crushed but cracks were observed. From the observation it seems to be beam pull out failure due to insufficient development length of reinforcement in joints. During earthquake, the horizontal movement of structure makes this condition worse and detached the beam member from column. Providing anchorage length between two existing concrete is very difficult. So not repairable.

1c)

From image observation cracks were found exactly at the Beam-column joint. Cracks in Beam developed through its entire width. Slab also developed more cracks along the beam width direction. In the strong column-weak beam design, beams are expected to form plastic hinges. It's a Plastic hinge failure. The damage occurred only in the joint zone first of all. Cyclic lateral loading & stress reversal at the joints led to the damage. Even the slab participated to its best to handle the Tension (Slab is severely cracked means it has undergone tension with its flange condition), But unable to control the damage. The joint can be strengthened.

2a)

In this case the top portion of the column concrete gets crushed and the reinforcement is yielded. Concrete damaged all around the column face and beams are safe. The location of column looks at edge of the building. No walls are built along the column means it is probably at Ground floor, for Parking Car movement access. It's a soft storey failure, technically Plastic hinge formation. Due to absence of Infill walls at the Ground floor the plastic hinge forms at the top of ground storey columns during Lateral movement. Based on the development of crush of concrete, it can either be repairable or non-repairable.

2b)

In this case concrete developed complete breakage diagonally. Longitudinal reinforcements are intact. Shear reinforcement spacing looks wider. It's a Pure Shear failure. This type of failure occurs due to large horizontal loads like wind load and seismic loads like earthquake loads. This type of failure can be avoided by providing the proper shear links and shear connectors and also increasing the size of the column in the direction of the shear which increases the shear capacity.Inadequate shear reinforcement compels concrete takes all the shear stresses.

2c)

In this case column failed completely at top of column. From the image observation it looks like there are two slabs connected to the column. One is at top and probably another one at mid height of the column. The wooden piles might be a post failure support after column failed, providing temporary prop to avoid collapse of the entire structure. It's a Short Column failure. The short column is subjected to compressive stresses and thus it fails due to crushing. An additional slab or a beam connected to a column in mid-height leads to this effect. This leads to failure especially if the connection is unintentional and not accounted in design. The failure given in the picture is not at all repairable.